SD cards. Data storage used in smaller portable devices but fairly old tech now.
SDHC cards. Probably the most popular memory cards now. Tt is a more capacious version of SD designed to house high-definition content but the same shape as an SD card. More modern version. An SD will play in a SDHC port but not vice versa.
SDXC cards. Same as SDHC but much larger capacity.
Micro SD/ Micro SDHC cards. Work the in same way as above but are even smaller and mostly used in mobile phones.
Card reader. Reads all memory cards, transferring data into the computer and between cards.